IgM antibodies against Treponema pallidum were investigated in the serum and in the CSF of 9 patients with symptomatic neurosyphilis, before the treatment and in several occasions after the treatment. Tests used were the FTA-Abs test, the IgM-solid phase hemadsorption test and an IgM-Elisa test. Titers of reactions decreased after treatment but they were still reactive in the blood and in the CSF during the second year after the treatment.